Mail is worked upon and active in the internal versions since some time, but for now the top priority is to get the main browser right.

This does not mean that there is no work done on the mail client, just that development is a bit slower.

Additionally, if a website or an extension breaks, it is normally no catastrophe - but that may not happen with mail, because that could destroy valuable user data (like an important mail), which must be avoided under all circumstances.

first of all, thanks for your hard work and good luck for your finish!

Since Vivaldi already is my main browser, I actually can't miss anything essential. However, I could imagine if jumping on the train right now, I would be really surprised by finding myself not being able to couple <ctrl>+ <t>with the "Next to tab"-option.